This invention relates to a liquid level sensor for measuring the level of an electrically conductive liquid in an electrically conductive, fiber-reinforced composite receptacle in which the receptacle construction itself comprises a component of the measuring apparatus.
In the past, a variety of methods have been employed for measuring the level or volume of liquid in a tank, including both mechanical and electrical methods. The mechanical methods have typically utilized some type of float which, because it stayed afloat on the surface of the liquid, could provide an indication by mechanical linkages of its position and thus of the level of the liquid.
Electrical methods of measuring liquid levels in tanks have included both (1) positioning electrical components within the tank, such as a column of switches which close when submerged in the liquid or underwater acoustic devices which determine the liquid level by reflected sonar signals, and (2) positioning some electrical components externally, such as capacitor plates to measure capacitance (where the level of liquid in the tank would affect the magnitude of the capacitance). In the latter arrangement, metal foil or wire screens have been placed on the exterior of the tanks to provide the capacitive sensing but this, of course, adds weight and additional components to the tank construction.
Various liquid level sensors are disclosed in U.S. Pat. Nos. 4,099,167, 5,017,909, 5,144,835, 5,049,826, 5,052,223, and 4,987,776.